1. Field of the Invention
The present invention relates to a starter for cranking an engine.
2. Related Art
A conventional starter is disclosed in Japanese Examined Utility Model Publication No. Sho 57-55970.
The starter is comprised of a planetary gear reduction mechanism for reducing the speed of starting motor rotation, and a one-way clutch for transmitting to an output shaft the motor rotation reduced by the planetary gear reduction mechanism. Planetary gears of the planetary gear reduction mechanism are rotatably mounted to the outer member of the one-way clutch by press-fitting or like mounting method. That is, the one-way clutch is unmovably arranged with respect to the output shaft so that only a pinion is fitted on the output shaft so as to be axially movable via a helical spline. Thus it becomes possible to decrease a force required to move the pinion as compared with the structure in which the one-way clutch and the pinion will move together on the output shaft, thereby enabling miniaturizing a magnet switch which is operated when the pinion moving force is required.
The center of the outer member will be determined by a relation of gears constituting the planetary gear reduction mechanism by directly securing, to the outer member, the pin supporting the corresponding planetary gear. However, since the outer member is a component part of the one-way clutch, the center of the outer member is determined by a relation between an inner member and a roller. It is, therefore, necessary that the center of the outer member determined on the reduction mechanism side corresponds to the center of the outer member determined on the clutch side; the function of the clutch and the life of the reduction mechanism largely depend upon the centering accuracy. Consequently, parts making up the reduction mechanism and the clutch are required to have a high dimensional accuracy, resulting in a high cost. Especially when miniaturization is pursued, further enhancement of the dimensional accuracy will be needed.
In another conventional starter having a planetary gear reduction mechanism and a shock absorbing device, an internal gear turns against a housing to absorb a shock applied to the reduction mechanism. When the internal gear turns in an eccentric condition because of backlash between gears, the outer peripheral surface of the internal gear slides frictionally on the inner peripheral surface of the housing. The housing generally made of an aluminum alloy or the like wears more than the internal gear made of resin reinforced by impregnation of glass fibers. Thus, aluminum wear powder is produced by the sliding of the outer periphery of the internal gear along the inner periphery of the housing, thereby causing the housing to become thinned and weakened. Further, the wear powder from the housing will enter bearings and gear engagement portion of the reduction mechanism, causing abnormal noise.
To counter this drawback, it is proposed in Japanese Unexamined Patent Publication No. 63-266166 to dispose wavy ring springs between the inner periphery of the hosing and the outer periphery of the internal gear as well as between the inner peripheries of the planetary gears and the outer periphery of support pins for the planetary gears. Thus, even when the internal gear turns eccentrically, the internal gear and the planetary gears are enabled by the resilient force of the springs to swing against respective radial centers and engage properly.
According to this starter, however, a relative movement occurs between the ring spring and the internal gear at the time of turning of the internal gear, because the ring spring is disposed stationary to the housing by the respective resiliency. Thus, friction occurs unavoidably between the contacting portions, i.e., between the ring spring and the internal gear.